Thermoplastic compositions, methods, apparatus, and uses

ABSTRACT

Thermoplastic polyurethane (TPU) compositions, methods for producing TPU compositions, methods of using TPU compositions, and apparatuses produced therefrom are disclosed. Disclosed TPU compositions include a thermoplastic polyurethane polymer, a heat stabilizer, a flow agent, and a filler material. The filler may be a glass fiber. Disclosed TPU compositions have improved thermal stability and improved flow properties suitable for injection molding of articles of manufacture having a large plurality of fine openings or pores. Articles produced from the composition have superior thermal stability, abrasion resistance, and chemical resistance. Example articles include screening members for vibratory screening machines. Further embodiments include compositions without heat stabilizers, flow agents, and filler materials, and compositions in which two TPU materials having different harnesses are combined to generate a material with a pre-determined hardness. Injection molded screen elements having openings from 25 to 150 microns and open screening area from 10% to 35% are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 15/965,363, filed on Apr. 27, 2018, which claims the benefit of U.S. Provisional Patent Applications No. 62/492,054, filed Apr. 28, 2017, and U.S. Provisional Patent Application No. 62/500,262, filed May 2, 2017, the entire contents of each of which are hereby incorporated by reference and the priority of which are hereby claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are part of this disclosure and are incorporated into the specification. The drawings illustrate example embodiments of the disclosure and, in conjunction with the description and claims, serve to explain various principles, features, or aspects of the disclosure. Certain embodiments of the disclosure are described more fully below with reference to the accompanying drawings. However, various aspects of the disclosure may be implemented in many different forms and should not be construed as being limited to the implementations set forth herein. Like numbers refer to like, but not necessarily the same or identical, elements throughout.

FIG. 1 is an isometric top view of a screen element, according to an embodiment.

FIG. 1A is a top view of the screen element shown in FIG. 1, according to an embodiment.

FIG. 1B is a bottom isometric view of the screen element shown in FIG. 1, according to an embodiment.

FIG. 1C is a bottom view of the screen element shown in FIG. 1, according to an embodiment.

FIG. 2 is an enlarged top view of a break out portion of the screen element shown in FIG. 1, according to an embodiment.

FIG. 3 is an isometric view of an end subgrid showing screen elements prior to attachment to the end subgrid, according to an embodiment.

FIG. 3A is an exploded isometric view of the end subgrid shown in FIG. 3 having the screen elements attached thereto, according to an embodiment.

FIG. 4 illustrates an example screening assembly that was generated from screening members and subgrid structures as described below with reference to FIGS. 1 to 3A, according to an embodiment.

FIG. 5 illustrates results of actual field testing of screening assemblies, according to an embodiment.

FIG. 6A illustrates a top view of a screen element that includes screening openings having rounded corners, according to an embodiment.

FIG. 6B illustrates a side view of the screen element of FIG. 6A, according to an embodiment.

FIG. 6C illustrates a top exploded view of a surface region of the screen element of FIG. 6A showing screening openings having rounded corners, according to an embodiment.

FIG. 7A illustrates a top view of a screen element that includes transversely aligned screening openings, according to an embodiment.

FIG. 7B illustrates an exploded top view of a portion of the screen element of FIG. 7A showing details of transversely aligned screening openings, according to an embodiment.

FIG. 7C illustrates a top view of a screen element that includes longitudinally aligned screening openings, according to an embodiment.

FIG. 7D illustrates an exploded top view of a portion of the screen element of FIG. 7C showing details of longitudinally aligned screening openings, according to an embodiment.

FIG. 8A illustrates cross sectional view of a surface element having a thickness of approximately 0.007 inch, according to an embodiment.

FIG. 8B illustrates cross sectional view of a first surface element having a thickness of approximately 0.005 inch, according to an embodiment.

FIG. 8C illustrates cross sectional view of a second surface element having a thickness of approximately 0.005 inch, according to an embodiment.

FIG. 9 illustrates a top view of a screen element and frame assembly with various regions that may be laser welded to an underlying subgrid, according to an embodiment.

FIG. 10 illustrates a vibrational amplitude profile of a screen element that is partially bonded to a subgrid, according to an embodiment.

DESCRIPTION OF EMBODIMENTS

This disclosure generally relates to compositions, apparatus, methods, and uses of thermoplastic polyurethanes (TPU). Disclosed embodiment TPU compositions may be used in injection molding processes to generate screening members for use in vibratory screening machines. Vibratory screening machines provide a capability to excite an installed screen such that materials placed upon the screen may be separated to a desired level. Oversized materials are separated from undersized materials. The disclosed compositions and screening members may be used in technology areas related to the oil industry, gas/oil separation, mining, water purification, and other related industrial applications.

Disclosed embodiments provide screening members that satisfy demanding requirements, such as: fine openings of approximately 43 μm to approximately 100 μm that effectively screen similar-sized particles; large area screens on the order of several square feet having large open screening area on the order of 30% to 35%; screens that are thermally and mechanically stable that can withstand severe conditions during operation, such as compression loading (e.g. forces from 1,500 lbs. to 3,000 lbs. applied to edges of screening members and vibrational accelerations of up to 10 G) and loading of high temperature materials (e.g. between 37° C. and 94° C.), with significant weight loads and severe chemical and abrasive conditions of the materials being screened.

Disclosed embodiment materials and methods provide a hybrid approach in which small screen elements are micro-molded using disclosed TPU materials to reliably generate fine features on the order of 43 μm to approximately 100 μm to yield screen elements having large open screening area. The disclosed TPU materials, as discussed in more detail below, include embodiments that feature optimized amounts of filler, heat stabilizer, and flow agent as additives to the appropriate thermoplastic polyurethane. These additives in turn allow for the small screen elements to be attached securely, such as via laser welding, to the subgrid structures to provide mechanical stability that may withstand the large mechanical loading and accelerations mentioned above. For example, glass fibers may be used as filler material, which allow for strengthening of the TPU material and in turn allow the screen elements to be securely attached to the subgrid structures with increased structural stability. However, addition of large amounts of glass fibers may lead to increased difficulty in laser welding, given that the refractive properties of the glass provide obstacles to the laser systems. Any amount of additive will also necessarily require dilution of the thermoplastic urethane. Similarly, a minimal but effective amount of heat stabilizer should be added, wherein the additive should be of sufficient amount to allow the end structure to withstand the addition of high-temperature materials as described above.

As discussed in more detail below, the amount of additives in the disclosed TPU compositions may also be varied based on the desired thickness T of the screen element surface elements, as discussed in detail in U.S. patent application Ser. Nos. 15/965,195 and 62/648,771, which are hereby incorporated by reference herein. For example, as discussed in U.S. patent application Ser. No. 15/965,195 in Paragraphs [00366] to [00373] and corresponding Tables 1 to 4, the thickness T of the screen element surface elements may be varied in an effort to maximize the percentage of open area on the overall screen assembly, which allows for increased effectiveness of the screening assembly when in use.

A plurality of these optimized subgrid structures may then be assembled into screening structures having large surface areas, on the order of several square feet. The screen assemblies based on the disclosed TPU compositions may be utilized, for example, in the manner described in U.S. patent application Ser. Nos. 15/965,195 and 62/648,771. For example, as outlined in U.S. patent application Ser. No. 15/965,195 in Paragraphs [0017] to [0021] of the Specification, the grid framework based upon the disclosed TPU compositions may provide the required durability against damage or deformation under the substantial vibratory load burdens it is subjected to when secured to a vibratory screening machine. The subgrids, when assembled to form the complete screen assembly, are strong enough not only to withstand the forces required to secure the screen assembly to the vibratory screening machine, but also to withstand the extreme conditions that may be present in the vibratory loading. As discussed in detail in Paragraphs [00280] to [00282] of the Specification of U.S. patent application Ser. No. 15/965,195, a method of securing the screen elements to the subgrid may include laser welding of the fusion bars arranged on the subgrids. The disclosed TPU compositions may therefore be utilized to create the referenced vibratory screening apparatus, capable of withstanding the extreme conditions discussed herein and in U.S. patent application Ser. No. 15/965,195.

Screen assemblies based on disclosed TPU compositions may also be configured to be mounted on vibratory screening machines described in U.S. Pat. Nos. 7,578,394; 5,332,101; 6,669,027; 6,431,366; and 6,820,748. Such screen assemblies may include: side portions or binder bars including U-shaped members configured to receive over mount type tensioning members, as described in U.S. Pat. No. 5,332,101; side portions or binder bars including finger receiving apertures configured to receive under mount type tensioning, as described in U.S. Pat. No. 6,669,027; side members or binder bars for compression loading, as described in U.S. Pat. No. 7,578,394; or may be configured for attachment and loading on multi-tiered machines, such as the machines described in U.S. Pat. No. 6,431,366.

Screen assemblies and/or screen elements based on disclosed TPU compositions may also be configured to include features described in U.S. Pat. No. 8,443,984, including the guide assembly technologies described therein and preformed panel technologies described therein. Still further, screen assemblies and screen elements based on disclosed TPU compositions may be configured to be incorporated into pre-screening technologies, compatible with mounting structures and screen configurations, described in U.S. Pat. Nos. 7,578,394; 5,332,101; 4,882,054; 4,857,176; 6,669,027; 7,228,971; 6,431,366; 6,820,748; 8,443,984; and 8,439,203. The disclosure of each of these patent documents, along with their related patent families and applications, and the patents and patent applications referenced in these documents, are expressly incorporated herein by reference in their entireties.

Example Screen Embodiments

Screening members fabricated from thermosetting and thermoplastic polymers are described in the above referenced patent documents (i.e., U.S. Provisional Patent Application Ser. Nos. 61/652,039 and 61/714,882; U.S. patent application Ser. No. 13/800,826; U.S. Pat. Nos. 9,409,209; 9,884,344; and U.S. patent application Ser. No. 15/851,099), the disclosures of which are incorporated herein by reference in their entireties.

FIGS. 1 to 3A illustrate example embodiment screening members generated by injection molding processes using disclosed TPU compositions. FIGS. 1 to 1C show an embodiment screen element 416 having substantially parallel screen element end portions 20, and substantially parallel screen element side portions 22, that are substantially perpendicular to the screen element end portions 20. Screen element 416 may include a plurality of tapered counter bores 470, which may facilitate extraction of screen element 416 from a mold, as described in greater detail in the above-referenced patent documents. Screen element 416 may further include location apertures 424, which may be located at a center of screen element 416 and at each of the four corners of screen element 416. Location apertures 424 are useful for attaching screen element 416 to subgrid structures, as described in greater detail below with reference to FIGS. 3 and 3A.

As shown in FIGS. 1 and 1A, screen element 416 has a screening surface 13 that includes solid surface elements 84 running parallel to the screen element end portions 20 and forming screening openings 86, as also shown in the close-up view of FIG. 2, as described in greater detail below.

FIGS. 1B and 1C show a bottom view of screen element 416 having a first screen element support member 28 extending between the end portions 20 and being substantially perpendicular to the end portions 20. FIG. 1B also shows a second screen element support member 30 perpendicular to the first screen element support member 28 extending between the side edge portions 22, being approximately parallel to the end portions 20 and being substantially perpendicular to the side portions 22. The screen element may further include a first series of reinforcement members 32 substantially parallel to the side edge portions 22, and a second series of reinforcement members 34 substantially parallel to the end portions 20. The end portions 20, the side edge portions 22, the first screen element support member 28, the second screen element support member 30, the first series reinforcement members 32, and the second series of reinforcement members 34, structurally stabilize the screen surface elements 84 and screening openings 86 during various loadings, including distribution of a compression force and/or vibratory loading conditions.

As shown in FIGS. 1B and 1C, screen element 416 may include one or more adhesion arrangements 472, which may include a plurality of extensions, cavities, or a combination of extensions and cavities. In this example, adhesion arrangement 472 is a plurality of cavity pockets. Adhesion arrangement 472 is configured to mate with complementary adhesion arrangements of a subgrid structure. For example, subgrid structure 414 (shown in FIGS. 3 and 3A) has a plurality of fusion bars, 476 and 478, that mate with cavity pockets 472 of screen element 416, as described in greater detail below with reference to FIGS. 3 and 3A.

As illustrated in FIG. 2, the screening openings 86 may be elongated slots having a length L along a first direction, and width W along a second direction, separated by surface elements 84 have a thickness T along the second direction. Thickness T may be varied depending on the screening application and configuration of the screening openings 86. Thickness T may be chosen to be approximately 0.003 inch to about 0.020 inch (i.e., about 76 μm to about 508 μm), depending on the open screening area desired, and the width W of screening openings 86. In an exemplary embodiment, the thickness T of the surface elements may be 0.015 inch (i.e., 381 μm). However, properties of disclosed TPU compositions allow formation of thinner surface elements, such as surface elements having a thickness T of 0.007 inch (i.e., 177.8 μm). The smaller the thickness, T, of the surface elements, the larger the screening area of the screen element. For example, a thickness T of 0.014 inch will provide a screen element that is about 10-15% open, while a thickness T of 0.003 inch will provide a screen element that is about 30-35% open, thus increasing open screening area.

As mentioned above, screening openings 86 have a width W. In exemplary embodiments, the width W may be approximately 38 μm to approximately 150 μm (i.e., about 0.0015 to about 0.0059 inch) between inner surfaces of each screen surface element 84. The length-to-width ratios of the openings may be from 1:1 (i.e. corresponding to round pores) to 120:1 (i.e., long narrow slots). In exemplary embodiments, openings may preferably be rectangular and may have a length-to-width ratio of between about 20:1 (e.g. length 860 μm; width 43 μm) to about 30:1 (i.e., length about 1290 μm, and width about 43 μm). The screening openings are not required to be rectangular but may be thermoplastic injection molded to include any shape suitable to a particular screening application, including approximately square, circular, and/or oval.

As described in greater detail below, for increased stability, the screen surface elements 84 may include integral fiber materials (e.g., glass fibers) which may run substantially parallel to end portions 20. Screen element 416 may be a single thermoplastic injection molded piece. Screen element 416 may also include multiple thermoplastic injection molded pieces, each configured to span one or more grid openings. Utilizing small thermoplastic injection molded screen elements 416, which are attached to a grid framework as described below, provides substantial advantages over prior screen assemblies, as described in greater detail in the above-referenced patent documents.

FIGS. 3 and 3A illustrate a process for attaching screen elements 416 to an end subgrid unit 414, according to an embodiment. Screen elements 416 may be aligned with end subgrid unit 414 via elongated attachment members 444 (of subgrid 414) that engage with location apertures 424 on an underside of the screen element 416 (e.g., see FIGS. 1 to 1C). In this regard, elongated attachment members 444 of subgrid 414 pass into screen element location apertures 424 of screen element 416. Elongated attachment members 444 of end subgrid 414 may then be melted to fill tapered bores of screen element attachment apertures 424, to thereby secure screen element 416 to the subgrid unit 414. Attachment via elongated attachment members 444 and screen element location apertures 424 is only one method for attaching screen member 416 to subgrid 414.

Alternatively, screen element 416 may be secured to end subgrid unit 414 using adhesives, fasteners and fastener apertures, laser welding, etc. As described above, fusion bars 476 and 478, of subgrid 414 (e.g., see FIGS. 3 and 3A), may be configured to fit into cavity pockets 472 of screen element 416 (e.g., see FIGS. 1 to 3C). Upon application of heat (e.g., via laser welding, etc.), fusion bars, 476 and 478, may be melted to form a bond between screen element 416 and subgrid 414 upon cooling.

Arranging the screen elements 416 on subgrids (e.g., subgrid 414), which may also be thermoplastic injection molded, allows for easy construction of complete screen assemblies with very fine screening openings. Arranging screen elements 416 on subgrids also allows for substantial variations in overall size and/or configuration of the screen assembly 10, which may be varied by including greater or fewer subgrids or subgrids having different shapes, etc. Moreover, a screen assembly may be constructed having a variety of screening opening sizes or a gradient of screening opening sizes simply by incorporating screen elements 416 with the different size screening openings onto subgrids and joining the subgrids to form a desired configuration.

The screens described above with reference to FIGS. 1 to 3, and disclosed in the above-reference patent documents, have small screening openings suitable for use as screening members. The disclosed TPU compositions additionally allow these screens to perform effectively in each of the following key areas: structural stability and durability; ability to withstand compression type loading; ability to withstand high temperatures; extended commercial life despite potential abrasion, cuts, or tearing; and fabrication methods that are not overly complicated, time consuming, or error-prone.

There is thus a need for improved TPU compositions having improved chemical properties that may be formed by injection molding into screening members and screening assemblies having improved physical properties.

Disclosed compositions generally include a TPU material, a heat stabilizer selected to optimize heat resistance of the composition, a flow agent selected to optimize use of the composition in injection molding, and a filler material selected to optimize rigidity of the resulting composite material. The filler may be included in an amount of less than about 10% by weight of the TPU. In one embodiment, the filler is provided in an amount of about 7% by weight of the TPU. In other exemplary embodiments, the filler is provided in amounts of less than about 7%, less than about 5%, or less than about 3%, of the weight of the TPU.

One example of a filler material includes glass fibers. Glass fibers may be introduced in an amount that allows use of the composition in injection molding, improves rigidity of the composition upon hardening, increases temperature resistance of the final product, and yet does not preclude laser welding of the composition to other materials.

An initial length of glass fibers may be between about 1.0 mm to about 4.0 mm. In an embodiment, glass fibers may have an initial length of about 3.175 mm (i.e., ⅛ inch). Glass fibers may also have a diameter of less than about 20 μm, such as between about 2 μm and about 20 μm. In one exemplary embodiment, the glass fibers have a diameter of between about 9 μm to about 13 μm. In further embodiments, the glass fibers have a diameter of between about 10 μm to about 14 μm. In further embodiments, glass fibers may have an initial length of ⅛ inch or less. For example, glass fibers may have an initial length of ⅛ inch, 1/16 inch, 1/32 inch, 1/64 inch, etc. In other embodiments, glass fibers may have an initial length that is in a range from approximate 200 μm to approximately 800 μm. After processing, glass fibers may have a length that is considerably smaller than the starting length. For example, glass fibers may have a final length of less than 1 μm. In further embodiments, glass fibers may have an initial length of approximately 4 mm and may have a final length after processing of approximately 0.5 mm.

The TPU material may be made from a low free isocyanate monomer prepolymer. In an example embodiment, the low free isocyanate monomer prepolymer may be chosen to be p-phenylene di-isocyanate. In further embodiments, other prepolymers may be chosen. The TPU may first be generated by reacting a urethane prepolymer with a curing agent. The urethane prepolymer may be chosen to have a free polyisocyanate monomer content of less than 1% by weight. In further embodiments, the TPU material may be a methylene diphenyl di-isocyanate (MDI) or a toluene di-isocyanate (TDI) modified polyester polyurethane. In various embodiments, a modified polyester is a material in which side chains have been modified to increase hydrolysis resistance.

The resulting material may then be thermally processed by extrusion at temperatures of 150° C., or higher, to form the TPU polymer. The urethane prepolymer may be prepared from a polyisocyanate monomer and a polyol including an alkane diol, polyether polyol, polyester polyol, polycaprolactone polyol, and/or polycarbonate polyol. In an example embodiment, the curing agent may include a diol, a triol, a tetrol, an alkylene polyol, a polyether polyol, a polyester polyol, a polycaprolactone polyol, a polycarbonate polyol, a diamine, or a diamine derivative.

According to an embodiment, the heat stabilizer, mentioned above, may be included in an amount of about 0.1% to about 5% by weight of the TPU. The heat stabilizer may be a sterically hindered phenolic antioxidant. The sterically hindered phenolic antioxidant may be pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (CAS Registry No. 6683-19-8). Optionally, an ultraviolet (UV) light stabilizer may be included. In some embodiments, the heat stabilizer will also serve as a UV light stabilizer.

According to an embodiment, the flow agent, mentioned above, may be included in an amount of about 0.1% to about 5% by weight of the TPU. The flow agent may be chosen to be an ethylene steramide wax. The ethylene steramide wax may include octadecanamide, N,N′-1,2-ethanediylbis (CAS Registry No. 110-30-5) and stearic acid (CAS Registry No. 57-11-4). In other embodiments, other flow agents may be chosen.

According to an embodiment, glass fibers, mentioned above, may have a diameter or width between about 2 to about 20 μm, between about 9 to about 13 μm, or may have a diameter or width about 11 μm. The glass fibers may have an initial length of between about 3.1 mm to about 3.2 mm. A final average length of the glass fibers, in a hardened state after injection molding, may be less than about 1.5 mm due to breakage of fibers during processing. In a final hardened state after injection molding, the fibers may be characterized by a distribution of lengths ranging from about 1.0 mm to about 3.2 mm, with some fibers remaining unbroken. In other embodiments, glass fibers may have initial and final lengths that are smaller. For example, glass fibers after processing may have an initial length that is ⅛ inch, 1/16 inch, 1/32 inch, 1/64 inch, etc. In other embodiments, glass fibers may have an initial length that is in a range from approximate 200 μm to approximately 800 μm. After processing, glass fibers may have a length that is considerably smaller than the initial length. For example, glass fibers may have a final length of less than 1 mm, less than 1 μm, etc.

Disclosed embodiments include methods of making and using TPU compositions suitable for use in injection molding of articles of manufacture having fine pores. Embodiment methods include reacting a TPU, a heat stabilizer, a flow agent, and a filler material, at a temperature greater than about 150° C., to generate a TPU composition. In other embodiments, a material may be generated by incorporating fewer components. For example, a composition may be generated that omits that heat stabilizer, omits the flow agent, omits the filler material, or that omits two or more of these components. The filler may include a glass fiber having a diameter of between about 2 μm to about 20 μm, in an amount selected to optimize rigidity of articles of manufacture molded from the TPU composition. The TPU may be polycarbonate TPU or may be a polyester or modified polyester TPU. The TPU may be a pre-polymer prior to the reacting step. The glass fiber may be present in an amount between about 1% to about 10% by weight of the TPU. In one embodiment, the glass fiber may be present in an amount of about 7% by weight of the TPU.

Articles of manufacture molded from compositions disclosed herein are suitable to be joined by various methods including laser welding. In this regard, the resulting articles may be laser welded to other articles, such as support structures.

Example articles of manufacture include screening members for vibratory shaker screens, as described above. Disclosed TPU material, described above, may then be used in an injection molding process to generate a screening member. In this regard, the TPU material may be introduced/injected into a suitably designed mold at an elevated temperature. The temperature may be chosen to be a temperature at which the TPU material has a sufficiently reduced viscosity to allow the material to flow into the mold. Upon cooling, the resulting solidified screening member may be removed from the mold.

The resulting screening member may be designed to have a plurality of openings having opening widths ranging from about 38 μm to about 150 μm. Screens with such openings may be used for removing particles from various industrial fluids to thereby filter/clean the fluids. Particles that are larger than widths of screening openings may be effectively removed. The desirable thermal properties of the TPU material allows screening members made from the TPU material to effectively screen particles at elevated temperatures (e.g., service temperatures of up to about 82 to 94° C.).

Characteristics of disclosed TPU compositions, and products generated therefrom, include temperature and flow characteristics that facilitate production of very fine, high-resolution structures using techniques such as injection molding. Resulting end products also have excellent thermal stability at elevated operating temperatures (e.g. up to about 94° C.). Resulting structures also exhibit sufficient structural rigidity to withstand compression loading while maintaining small openings that allow for screening of micron-scale particulate matter. Structures generated from disclosed TPU materials also exhibit cut, tear, and abrasion resistance, as well as chemical resistance in hydrocarbon-rich environments (e.g. environments including hydrocarbons such as diesel fuel).

Thermoplastic Polyurethanes

Disclosed embodiments provide thermoplastic compositions including polyurethanes, which are a class of macromolecular plastics known as polymers. Generally, polymers, such as polyurethanes, include smaller, repeating units known as monomers. Monomers may be chemically linked end-to-end to form a primary long-chain backbone molecule with or without attached side groups. In an example embodiment, polyurethane polymers may be characterized by a molecular backbone including carbonate groups (—NHCO₂), for example.

While generally categorized as plastics, thermoplastic compositions include polymer chains that are not covalently bonded, or crossed linked, to one another. This lack of polymer chain crosslinking allows thermoplastic polymers to be melted when subjected to elevated temperatures. Moreover, thermoplastics are reversibly thermoformable, meaning that they may be melted, formed into a desired structure, and re-melted in whole or in part at a later time. The ability to re-melt thermoplastics allows optional downstream processing (e.g., recycling) of articles generated from thermoplastics. Such TPU based articles may also be melted at discrete locations by applying a heat source to a specific location on an article. In this regard, articles generated from disclosed TPU composition are amenable to joining using welding (e.g., laser welding) to effectively secure TPU-based screening members to suitable screening frames.

Disclosed TPU materials exhibit desirable properties under extreme conditions of temperature and harsh chemical environments. In exemplary embodiments, such TPU materials may be made from a prepolymer. An example prepolymer may include a p-phenylene di-isocyanate (PPDI) with low free isocyanate content. In other embodiments, different suitable prepolymers may be used.

Disclosed herein are thermoplastic polyurethanes suitable for use in fabricating the disclosed screen elements. The disclosed polyurethanes comprise hard and soft segments which can be artfully manipulated by the fabricator to produce final polyurethanes having the desired properties, for example, abrasion control, flowable during injection molding, anti-fracture properties and the like. In one aspect the disclosed polyurethanes, as described herein, have from a 85 Shore A to 59 Shore D.

The disclosed thermoplastic polyurethanes can be fabricated from a prepolymer and a curing agent. The prepolymer, as well as, the curing agent can be purchased from chemical suppliers or the prepolymer and curing agent can be synthesized by the fabricator.

Prepolymers

The disclosed prepolymer can comprise any urethane forming unit. The urethane forming units comprise two types: aryl diisocyanates and aliphatic diisocyanates. In general the urethane forming unit is reacted with a polyol that serves to connect two diisocyanate moieties. For example, the prepolymer can be formed by the following reaction:

wherein R is a carbon skeleton of 2 to 15 carbon atoms, and/or a bivalent aromatic radical of 6 to 18 carbon atoms.

In one embodiment R is an alkylene unit having 2 to 15 carbon atoms, i.e., from 2 to 15 methylene units, —(CH₂)₂— to —(CH₂)₁₅—. As such, R can comprise from 2 to 15 methylene units, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 methylene units. Non-limiting examples of ONC—R—NCO include 1,6-hexamethylene diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI) and 4,4′-diisocyanato dicyclohexylmethane.

In another embodiment R is a bivalent aromatic radical of 6 to 18 carbon atoms. In one iteration, R is formed from a methylene diphenyl diisocyanate (MDI) wherein R has the formula:

In a further embodiment, R can be a 1,2-phenylene. 1,3-phenylene, of a 1,4-phenylene unit having the formula:

Utilization of these R units results in polyphenylene diisocyanate prepolymer units.

Linking R¹ Units

The disclosed R¹ units can be alkylene unit having 2 to 10 carbon atoms, i.e., from 2 to 10 methylene units, —(CH₂)₂— to —(CH₂)₁₀—. As such, R¹ can comprise from 2 to 10 methylene units, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10 methylene units. Non-limiting examples of HO—R—OH include 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pemtanediol, 1,6-hexanediol, 1,7-heptanediol, 1-8-octanediol, 1,9-nonanediol, and 1,10-decanediol.

Polycaprolactone Diol-Based Polyester Prepolymers

The disclosed R¹ units can be derived from a caprolactone diol unit having the formula:

A non-limiting example of a polycaprolactone diol prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about 8.

A further non-limiting example of a prepolymer derived from a polycaprolactone diol unit has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about 8.

Polyglycidyl Diol Prepolymers

The disclosed R¹ units can be derived from a polyglycidyl diol having the formula:

A non-limiting example of a polyglycidyl diol prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about 8.

A further non-limiting example of a prepolymer derived from a polyglycidyl diol unit has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about 8.

Polylactide Diol Prepolymers

The disclosed R¹ units can be derived from a polylactide diol having the formula:

A non-limiting example of a polylactide diol prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about 8.

A further non-limiting example of a prepolymer derived from a polylactide diol unit has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about 8.

Polycarbonate Prepolymers

The disclosed R¹ units can be derived from diols having the formula:

A non-limiting example of a polycarbonate diol prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about 8.

Polyalkylene Diol Prepolymers

The disclosed R¹ units can be derived from polyalkylene diols having the formula:

HO—(CH₂)_(z)—OH

wherein the index z is from about 4 to about 25.

One embodiment of the disclosed polyalkylene diol prepolymers has the formula:

A non-limiting example of a polyalkylene diol prepolymer has the formula:

Polyether Diol Prepolymers

1. Polyethylene Glycol Prepolymers

The disclosed R¹ units can be derived from a polyether diol. In one embodiment, the R¹ comprises a polyethylene glycol having the formula:

HO—[(CH₂CH₂O)_(y)]CH₂CH₂—OH

wherein the index y is from about 4 to about 25. The following is a non-limiting embodiment of the disclosed PEG prepolymers:

2. Polypropylene Glycol Prepolymers

In another embodiment of the disclosed polyether diol prepolymers, the disclosed R¹ units can be derived from a polyethylene glycol having the formula:

wherein the index y is from about 4 to about 25. The following is a non-limiting embodiment of the disclosed PPG prepolymers:

Curing Agents

The disclosed prepolymers are further reacted with one or more curing agents to form the disclosed thermoplastic polyurethanes having the formula:

wherein the index m is from 3 to 20. The curing agents are chosen from polycaprolactone diols, polyglycidyl diols, polylactide diols, polycarabonate diols, polyethylene glycols, polypropylene glycols, or polyalkylene diols.

The disclosed R² units are chosen from:

i) Polyester polyurethane forming unit:

ii) Polyester polyurethane forming unit:

iii) Polyester polyurethane forming unit:

iv) Polycarbonate polyurethane forming unit:

v) Polyalkylene polyurethane forming unit:

vi) Polyether polyurethane forming unit:

or

vii) Polyether polyurethane forming unit:

In some embodiments the curing agent can be a repeating or non-repeating polyol. For example, a branched polyol having the formula:

can react with three prepolymer units thereby providing a means for crosslinking the polyurethane chains. In one iteration a non-stoichiometric amount of a first curing agent can be combined with a polyol in an amount that provides the necessary hydroxyl units to consume the available isocyanate groups.

As stated herein above, in one aspect the disclosed polyurethanes, as described herein, have from a 85 Shore A to 59 Shore D durometer value. The desired hardness of the resulting thermoplastic polyurethanes can be achieved either by the artful selection of the disclosed R, R¹ and R² units together with the proper selection of the indices x, y, m and n. Another disclosed method is to select two polymers having different Shore D durometer values and to admix the two polymers to obtain an intermediary Shore D durometer hardness value between the values of the two polymers. In addition, a 95 Shore A could convert to a 45 Shore D which can be combined with a 56 Shore D to form a polymer having an intermediate hardness.

Disclosed herein is a screen element, comprising:

i) a first thermoplastic polyurethane having a first hardness; and

ii) a second thermoplastic polyurethane having a second hardness;

wherein the first and second polyurethanes are combined to form a final thermoplastic polyurethane having a hardness of from approximately 85 Shore A to 59 Shore D; wherein the screen element is a single injection molded piece having a plurality of openings from 43 μm to 100 μm; and wherein the amount of openings is from 10% to 35% of the screen element.

The first polyurethane and the second polyurethane are formed by reacting a prepolymer having the formula chosen from:

wherein the index x is from 2 to about 6, the index y is from about 4 to about 25, index z is from about 4 to about 25, and the index n is from 2 to about 8; and wherein further the prepolymer contains less than 0.1% by weight of excess isocyanate moieties; with a curing agent, wherein the curing agent is chosen from polycaprolactone diols, polyglycidyl diols, polylactide diols, polycarabonate diols, polyethylene glycols, polypropylene glycols, or polyalkylene diols.

Example TPU materials may be generated as follows. A TPU polymer may be produced by reacting a urethane prepolymer, having a free polyisocyanate monomer content of less than 1% by weight, with a curing agent. The resulting material may then be thermally processed by extrusion at temperatures of 150° C. (or higher) to form the TPU material. The urethane prepolymer may be prepared from a polyisocyanate monomer and a polyol including an alkane diol, a polyether polyol, a polyester polyol, a polycaprolactone polyol, and/or a polycarbonate polyol. The curing agent may include a diol, a triol, a tetrol, an alkylene polyol, a polyether polyol, a polyester polyol, a polycaprolactone polyol, a polycarbonate polyol, a diamine, or a diamine derivative.

Disclosed TPU materials may then be combined with a heat stabilizer, a flow agent, and a filler material, according to various embodiments. In further embodiments, other additives may be included as needed.

Generally, disclosed embodiments provide TPU compositions that may be formed by reacting a polyol with a polyisocyanate and polymer chain-extender. Example embodiments include synthetic production methods and processes for making TPU compositions. Disclosed methods may include reacting monomers, curing agents, and chain extenders in a reaction vessel to form pre-polymers. Disclosed methods may further include forming pre-polymers by reacting a di-isocyanate (OCN—R—NCO) with a diol (HO—R—OH). Formation of a pre-polymer includes chemically linking two reactant molecules to produce a chemical product having an alcohol (OH) at one position and an isocyanate (NCO) at another position of the product molecule. In an embodiment, a disclosed pre-polymer includes both a reactive alcohol (OH) and a reactive isocyanate (NCO). Articles generated using the TPU compositions disclosed herein may be fully cured polymer resins that may be stored as a solid plastic.

Disclosed embodiments provide pre-polymers that may be prepared from a polyisocyanate monomer and a curing agent. Non-limiting examples of curing agents may include ethane diol, propane diol, butane diol, cyclohexane dimethanol, hydroquinone-bis-hydroxyalkyl (e.g., hydroquinone-bis-hydroxyethyl ether), diethylene glycol, dipropylene glycol, dibutylene glycol, triethylene glycol, etc., dimethylthio-2,4-toluenediamine, di-p-aminobenzoate, phenyldiethanol amine mixture, methylene dianiline sodium chloride complex, etc.

In example embodiments, a polyol may include an alkane diol, polyether polyol, polyester polyol, polycaprolactone polyol, and/or polycarbonate polyol. In certain embodiments, the polyol may include a polycarbonate polyol either, alone or in combination with other polyols.

Heat Stabilizers

Disclosed heat/thermal stabilizers may include additives such as organosulfur compounds, which are efficient hydroperoxide decomposers that thermally stabilize polymers. Non-limiting example heat stabilizers include: organophosphites such as triphenyl phosphite, tris-(2,6-dimethylphenyl) phosphite, tris-(mixed mono- and di-nonylphenyl) phosphite etc.; phosphonates such as dimethylbenzene phosphonate, etc.; phosphates such as trimethyl phosphate, etc.; dihexylthiodiformate dicyclohexyl-10,10′-thiodidecylate dicerotylthiodiformate dicerotyl-10,10′-thiodidecylate dioctyl-4,4-thiodibutyrate diphenyl-2,2′-thiodiacetate (thiodiglycolate) dilauryl-3,3′-thiodipropionate distearyl-3,3′-thiodipropionate di(p-tolyl)-4,4′-thiodibutyratelauryl myristyl-3,3′-thiodipropionate palmityl stearyl-2,2′-thiodiacetate dilauryl-2-methyl-2,2′-thiodiacetatedodecyl 3-(dodecyloxycarbonylmethylthio) propionate stearyl 4-(myri styloxycarbonylmethylthio) butyrate diheptyl-4,4-thiodibenzoate dicyclohexyl-4,4′-thiodicyclohexanoate dilauryl-5,5′-thio-4-methylbenzoate; and mixtures thereof etc. When present, thermal stabilizers may be included in amounts of about 0.0001% to about 5% by weight, based on the weight of the base-polymer component used in the TPU composition. Inclusion of organosulfur compounds may also improve thermal stability of TPU compositions as well as articles produced therefrom.

In an exemplary embodiment, a heat stabilizer may be a sterically hindered phenolic antioxidant, such as Pentaerythritol Tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (CAS Registry No. 6683-19-8). In example embodiments, the heat stabilizer may be included in amounts ranging from about 0.1% to about 5% by weight of the TPU.

Flow Agents

Flow agents are used to enhance flow characteristics of TPU materials so that such TPU materials may be easily injected into a mold. Injection times for disclosed TPU materials are preferably between about 1 to about 2 seconds. In an embodiment, flow times averaging about 1.6 seconds have been achieved. Flow agents are used to achieve such injection times.

Disclosed TPU compositions may include flow agents that improve lubrication to increase the flow of melted polymer compositions relative to an external surface (i.e., to increase external flow). Flow agents may also increase the flow of individual polymer chains within a thermoplastic melt (i.e., to increase internal flow).

Disclosed embodiments provide TPU compositions that may include an internal flow agent that may be readily compatible with the polymer matrix. For example, the internal flow agent may have a similar polarity that improves the ease of flow of the melt by preventing internal friction between the individual particles of the polymer. In certain embodiments, TPU compositions including internal flow agents may improve molding characteristics. For example, in a specific embodiment, TPU compositions may be used to produce articles having small or very small openings. In another embodiment, TPU compositions may be used to produce articles having very fine openings by injection molding. In further embodiments, the improved flow of the TPU compositions allows production of high-resolution articles having small or very small openings.

Disclosed embodiments provide TPU compositions that may include an external flow agent that may be more or less compatible with the polymer matrix of a TPU composition. For example, an external flow agent may have a different polarity relative to the TPU composition polymer. Since external flow agents may not be compatible with the TPU polymer matrix of the composition, external flow agents may act as an external lubricating film between the polymer and hot metallic surfaces of processing machines. Thus, external lubricants may prevent a polymer melt from adhering to machine parts (e.g., such as an extruder), and may also reduce the force required to remove a cured polymer from a mold (i.e., may improve demolding) in the case of injection molding.

Non-limiting, examples of flow agents that may be included in TPU compositions include amines (e.g., ethylene bisstearamide), waxes, lubricants, talc, and dispersants. Disclosed embodiments provide TPU compositions that may also include one or more inorganic flow agents such as hydrated silicas, amorphous alumina, glassy silicas, glassy phosphates, glassy borates, glassy oxides, titania, talc, mica, fumed silicas, kaolin, attapulgite, calcium silicates, alumina, and magnesium silicates. The amount of flow agent may vary with the nature and particle size of the particular flow agent selected.

In exemplary embodiments, the flow agent may be a wax, such as an ethylene steramide wax. An ethylene steramide wax may include octadecanamide, N,N′-1,2-ethanediylbis (C₃₈H₇₆N₂O₂; CAS Registry No. 100-30-5) and stearic acid [CH₃(CH₂)₁₆COOH; CAS Registry No. 57-11-4]. In exemplary embodiments, the flow agent may be present in amounts from about 0.1% to about 5% by weight of the TPU.

Improved flow characteristics of TPU compositions may be achieved by reducing or eliminating the presence of certain compounds, such as calcium stearate, for example.

Fillers

As described above, disclosed embodiments provide TPU compositions that may also include fillers that may include inorganic materials. Fillers strengthen and stiffen the TPU based material, enhancing properties of objects injection molded from the TPU material. For example, fillers help to maintain shapes of small openings, holes, or pores, formed in objects injection molded from the TPU composition. In some embodiments, for example, the fibers allow transmission of light for use in laser welding of molded TPU components to support structures.

In exemplary embodiments, glass fibers may be used as filler material, as described above. Glass fibers may take the form of solid or hollow glass tubes. In exemplary embodiments, glass tubes may have a diameter (or width, if not round) of between about 2 μm to about 20 μm. In an exemplary embodiment, glass fibers may have a diameter (or width, if not round) of between about 9 μm to about 13 μm. In an embodiment, glass fibers may have a 11 μm diameter or width. Glass fibers may have an initial length of between about 3.0 mm to about 3.4 mm. In an exemplary embodiment, glass fibers may have an initial length of ⅛ inch (i.e., 3.175 mm). In further embodiments, glass fibers may have an initial length that is 1/16 inch, 1/32 inch, 1/64 inch, etc. During processing of the TPU material, however, glass fibers may break and thereby become shorter. In a hardened state after injection molding, glass fibers may have an average length of less than about 1.5 mm, with a range of most fibers being between about 1.0 mm to about 3.2 mm. After processing, glass fibers may have a length that is considerably smaller than the starting length. For example, glass fibers may have a final length of less than 1 μm. Some of the fibers retain their original length, but most are broken into smaller pieces.

To allow laser welding of the TPU composition, it is desirable to use as little glass fiber as possible. Too much glass fiber leads to an unacceptably high amount of reflection/refraction of laser light. Additionally, desired properties of the TPU composition may degrade with increasing glass fiber content. Glass fibers having a sufficiently large diameter may work better for laser weldable compositions. Such large diameter fibers may also provide desirable strengthening and stiffening properties. The diameter of glass fibers should not be too large, however, as desirable flow properties may degrade with increasing diameter of glass fibers, reducing the suitability of the resulting composition for injection molding.

Glass fiber filler materials should not contain fibers having a diameter of greater than 50 μm, and should preferably have a diameter of less than 20 μm, in compositions developed for injection molding of structures having features on a sub-millimeter scale. Carbon fibers should be avoided in that they may not work for laser welding because they are not translucent. TPU based objects that are designed to be joinable via laser welding may have optical properties that allow laser light to pass through the TPU material. As such, laser light may pass through the TPU object and may hit an adjacent structure such as to a nylon subgrid. The nylon material of the subgrid is a thermoplastic having a dark color that absorbs laser light and may thereby be heated by the laser. Upon absorption of laser light, the TPU and the adjacent nylon may be heated to a temperature above their respective melting temperatures. In this way, both materials may be melted, and upon cooling, a mechanical bond may be formed at an interface between the TPU and the nylon, thereby welding the components together.

Disclosed embodiments provide TPU compositions that may also include particulate fillers, which may be of any configuration including, for example, spheres, plates, fibers, acicular (i.e., needle like) structures, flakes, whiskers, or irregular shapes. Suitable fillers may have an average longest dimension in a range from about 1 nm to about 500 μm. Some embodiments may include filler materials with average longest dimension in a range from about 10 nm to about 100 μm. Some fibrous, acicular, or whisker-shaped filler materials (e.g., glass or wollastonite) may have an average aspect ratio (i.e., length/diameter) in a range from about 1.5 to about 1000. Longer fibers may also be used in further embodiments.

Plate-like filler materials (e.g., mica, talc, or kaolin) may have a mean aspect ratio (i.e., mean diameter of a circle of the same area/mean thickness) that is greater than about 5. In an embodiment, plate-like filter materials may have an aspect ratio in a range from about 10 to about 1000. In a further embodiment, such plate-like materials may have an aspect ratio in a range from about 10 to about 200. Bimodal, trimodal, or higher mixtures of aspect ratios may also be used. Combinations of fillers may also be used in certain embodiments.

According to an embodiment, a TPU composition may include natural, synthetic, mineral, or non-mineral filler materials. Suitable filler materials may be chosen to have sufficient thermal resistance so that a solid physical structure of the filler material may be maintained, at least at the processing temperature of the TPU composition with which it is combined. In certain embodiments, suitable fillers may include clays, nanoclays, carbon black, wood flour (with or without oil), and various forms of silica. Silica materials may be precipitated or hydrated, fumed or pyrogenic, vitreous, fused or colloidal. Such silica materials may include common sand, glass, metals, and inorganic oxides. Inorganic oxides may include oxides of metals in periods 2, 3, 4, 5 and 6 of groups IB, IIB, IIIA, IIIB, IVA, IVB (except carbon), VA, VIA, VIIA, and VIII, of the periodic table.

Filler materials may also include oxides of metals, such as aluminum oxide, titanium oxide, zirconium oxide, titanium dioxide, nanoscale titanium oxide, aluminum trihydrate, vanadium oxide, magnesium oxide, antimony trioxide, hydroxides of aluminum, ammonium, or magnesium. Filler materials may further include carbonates of alkali and alkaline earth metals, such as calcium carbonate, barium carbonate, and magnesium carbonate. Mineral based materials may include calcium silicate, diatomaceous earth, fuller earth, kieselguhr, mica, talc, slate flour, volcanic ash, cotton flock, asbestos, and kaolin.

Filler materials may further include alkali and alkaline earth metal sulfates, for example, sulfates of barium and calcium sulfate, titanium, zeolites, wollastonite, titanium boride, zinc borate, tungsten carbide, ferrites, molybdenum disulfide, cristobalite, aluminosilicates including vermiculite, bentonite, montmorillonite, Na-montmorillonite, Ca-montmorillonite, hydrated sodium calcium aluminum magnesium silicate hydroxide, pyrophyllite, magnesium aluminum silicates, lithium aluminum silicates, zirconium silicates, and combinations of the above-described filler materials.

Disclosed embodiments provide TPU compositions that may include fibrous fillers such as glass fibers (as described above), basalt fibers, aramid fibers, carbon fibers, carbon nanofibers, carbon nanotubes, carbon buckyballs, ultra-high molecular weight polyethylene fibers, melamine fibers, polyamide fibers, cellulose fiber, metal fibers, potassium titanate whiskers, and aluminum borate whiskers.

In certain embodiments, TPU compositions may include glass fiber fillers, as described above. Glass fiber fillers may be of E-glass, S-glass, AR-glass, T-glass, D-glass and R-glass. In certain embodiments, the glass fiber diameter may be within a range from about 5 μm to about 35 μm. In other embodiments, the diameter of the glass fibers may be in a range from about 9 to about 20 μm. In further embodiments, glass fibers may have a length of about 3.2 mm or less. As described above, TPU compositions including glass fillers may confer improved thermal stability to the TPU compositions and articles produced them.

Disclosed embodiments may include compositions containing a glass filler with concentrations in a range from about 0.1% to about 7% by weight. Embodiments may also include glass filler at concentrations ranging from about 1% to about 2%; about 2% to about 3%; 3% to about 4%; about 4% to about 5%; about 5% to about 6%; about 6% to about 7%; about 7% to about 8%; about 8% to about 9%; about 9% to about 10%; about 10% to about 11%; about 11% to about 12%; about 12% to about 13%; about 13% to about 14%; about 14% to about 15%; about 15% to about 16%; about 16% to about 17%; about 17% to about 18%; about 18% to about 19%; and about 19% to about 20%. In certain embodiments a glass filler concentration may be about 1%. In certain embodiments a glass filler concentration may be about 3%. In certain embodiments a glass filler concentration may be about 5%. In certain embodiments a glass filler concentration may be about 7%. In certain embodiments a glass filler concentration may be about 10%.

As described above, embodiments may include glass filler material wherein individual glass fibers may have a diameter or width in a range from about 1 μm to about 50 μm. In certain embodiments, the glass filler may be characterized by a narrow distribution of fiber diameters such that at least 90% of the glass fibers have a specific diameter or width. Other embodiments may include a glass filler having a broader distribution of diameters or widths spanning a range from about 1 μm to about 20 μm. Further embodiments may include glass filler having a glass fiber diameter or width distribution spanning a range: from about 1 μm to about 2 μm; from about 2 μm to about 3 μm; from about 3 μm to about 4 μm; from about 4 μm to about 5 μm; from about 5 μm to about 6 μm; from about 6 μm to about 7 μm; from about 7 μm to about 8 μm; from about 8 μm to about 9 μm; from about 9 μm to about 10 μm; from about 10 μm to about 11 μm; from about 11 μm to about 12 μm; from about 12 μm to about 13 μm; from about 13 μm to about 14 μm; from about 14 μm to about 15 μm; from about 15 μm to about 16 μm; from about 16 μm to about 17 μm; from about 17 μm to about 18 μm; from about 18 μm to about 19 μm; and from about 19 μm to about 20 μm. In certain embodiments the glass filler may have a diameter or width distribution centered about a specific value. For example, the specific diameter or width value may be 10 μm±2 μm, according to an embodiment.

TPU compositions may include glass fiber fillers that include a surface treatment agent and optionally a coupling agent, according to an embodiment. Many suitable materials may be used as a coupling agent. Examples include silane-based coupling agents, titanate-based coupling agents, or a mixture thereof. Applicable silane-based coupling agents, for example, may include aminosilane, epoxysilane, amidesilane, azidesilane, and acrylsilane.

Disclosed embodiments provide TPU compositions that may also include other suitable inorganic fibers such as: carbon fibers, carbon/glass hybrid fibers, boron fibers, graphite fibers, etc. Various ceramic fibers can also be utilized such as alumina-silica fibers, alumina fibers, silicon carbide fibers, etc. Metallic fibers, such as aluminum fibers, nickel fibers, steel, stainless steel fibers, etc., may also be used.

Disclosed TPU compositions may be generated by a process in which TPU reactants may be combined with filler materials (e.g., fiber fillers) and other optional additives. The combination of materials may then be physically mixed in a mixing or blending apparatus.

An example mixing or blending apparatus may include: a Banbury, a twin-screw extruder, a Buss Kneader, etc. In certain embodiments, filler and base TPU composition materials may be mixed or blended to generate a TPU composition blend having fibers incorporated therein. The resulting TPU composition having fillers (e.g., glass fibers), and optionally other additional additives, may be cooled to generate a solid mass. The resulting solid mass may then be pelletized or otherwise divided into suitable size particles (e.g., granulated) for use in an injection molding process. The injection molding process may be used to generate an article of manufacture such as a screen or screen element.

Optional additives to TPU compositions, mentioned above, may include dispersants. In certain embodiments, dispersants may help to generate a uniform dispersion of base TPU composition and additional components such as fillers. In certain embodiments, a dispersant may also improve mechanical and optical properties of a resulting TPU composition that includes fillers.

In certain embodiments, waxes may be used as dispersants. Non-limiting examples of wax dispersants, suitable for use in disclosed TPU compositions, include: polyethylene waxes, amide waxes, and montan waxes. TPU compositions disclosed herein may include an amide wax dispersant, such as N,N-bis-stearyl ethylenediamine. The use of such a wax dispersant may increase thermal stability of the TPU composition yet may have little impact on polymer transparency. As such, inclusion of dispersants in disclosed TPU compositions may have at least to desirable effects: (1) improved thermal stability of compositions and articles produced therefrom, and (2) desirable optical properties that are suitable for downstream processing including laser welding.

Disclosed TPU compositions may further include antioxidants, according to an embodiment. Antioxidants may be used to terminate oxidation reactions, that may occur due to various weathering conditions, and/or may be used to reduce degradation of a TPU composition. For example, articles formed of synthetic polymers may react with atmospheric oxygen when placed into service. In addition, articles formed of synthetic polymers may undergo auto-oxidization due to free-radical chain reactions. Oxygen sources (e.g., atmospheric oxygen, alone or in combination with a free radical initiator) may react with substrates included in disclosed TPU compositions. Such reactions may compromise integrity of the TPU composition and articles produced therefrom. Inclusion of antioxidants, therefore, may improve chemical stability of TPU compositions as well as improving chemical stability of articles generated therefrom.

Polymers may undergo weathering in response to absorption of UV light that causes radical initiated auto-oxidation. Such auto-oxidation may lead to cleavage of hydroperoxides and carbonyl compounds. Embodiment TPU compositions may include Hydrogen-donating antioxidants (AH), such as hindered phenols and secondary aromatic amines. Such AH additives may inhibit oxidation of TPU compositions by competing with organic substrates for peroxy radicals. Such competition for peroxy radicals may terminate chain reactions and thereby stabilize or prevent further oxidation reactions. Inclusion of antioxidants in disclosed TPU compositions may inhibit formation of free radicals. In addition to AH being a light stabilizer, AH may also provide thermal stability when included in disclosed TPU compositions. Accordingly, certain embodiments may include additives (e.g., AH) that enhance stability of polymers exposed to UV light and heat. Articles generated from disclosed TPU compositions having antioxidants may, therefore, be resistant to weathering and have improved function and/or lifespan, when deployed under high-temperature conditions, relative to articles generated from TPU compositions lacking antioxidants.

Disclosed TPU compositions may further include UV absorbers, according to an embodiment. UV absorbers convert absorbed UV radiation to heat by reversible intramolecular proton transfer reactions. In some embodiments, UV absorbers may absorb UV radiation that would otherwise be absorbed by the TPU composition. The resulting reduced absorption of UV rays by the TPU composition may help to reduce UV radiation induced weathering of the TPU composition. Non-limiting example UV-absorbers may include oxanilides for polyamides, benzophenones for polyvinyl chloride (PVC), and benzotriazoles and hydroxyphenyltriazines for polycarbonate materials. In an embodiment, 2-(2′-Hydroxy-3′-sec-butyl-5′-tert-butylphenyl)benzotriazole may provide UV light stabilization for polycarbonate, polyester, polyacetal, polyamides, TPU materials, styrene-based homopolymers, and copolymers. These and other UV absorbers may improve the stability of disclosed TPU compositions and articles produced therefrom, according to various embodiments.

TPU compositions may further include anti-ozonants which may prevent or slow degradation of TPU materials caused by ozone gas in the air (i.e., may reduce ozone cracking). Non-limiting exemplary embodiments of antiozonates may include: p-Phenylenediamines, such as 6PPP (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine) or IPPD (N-isopropyl-N′-phenyl-p-phenylenediamine); 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, (ETMQ) ethylene diurea (EDU), and paraffin waxes that may form a surface barrier. These and other antiozonants may improve the stability of disclosed TPU compositions as well as articles produced therefrom, according to various embodiments.

According to an embodiment, an example mixture may be prepared as follows. The starting material may be chosen to be a polycarbonate-based thermoplastic polyurethane. A filler material may be chosen to be small diameter (as described above) glass fibers included in an amount from between about 3% and about 10% by weight. A flow agent may then be chosen to be included in an amount of between about 0.1% to about 5% by weight. In this example, the flow agent may be taken to be a mixture of octadecanamide, N,N′-1,2-ethanediylbis and stearic acid. A thermal-stabilizing agent may be chosen to be pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) included in an amount of between about 0.1% to about 5% by weight. The above-described thermoplastic mixture may then be injected into bulk thermoplastic rods then pelletized for downstream injection molding.

Methods

Disclosed embodiments provide methods and processes for generating TPU compositions. Disclosed methods may include reacting (i.e., linking) pre-polymer units including an alcohol (OH) and an isocyanate (NCO) to effectively “grow” and/or extend a polymer chain or backbone. For example, in an embodiment, a TPU composition may be prepared by reacting a polyurethane pre-polymer and a curing agent, typically at temperatures from about 50° C. to about 150° C., for example, or from about 50° C. to about 100° C. Temperatures outside these ranges may also be employed in certain embodiments.

Disclosed TPU compositions may be melted and formed into a desired shape, for example, by injection molding. Disclosed methods may further include a post curing step including heating the TPU material at temperatures from about 50° C. to about 200° C., or from about 100° C. to about 150° C., for a predetermined period of time. For example, TPU materials may be heated for about 1 hour to about 24 hours. Alternatively, various methods may include an extrusion step wherein a post-cured TPU composition may be extruded at temperatures from about 150° C. to about 270° C., or from about 190° C. or higher, to render the TPU composition in an intermediate form. The intermediate form may be suitable for downstream processing to generate a final form, such as a TPU based screen element.

Disclosed methods may include a variety of additional processing operations. For example, a disclosed method or process may include: reacting a polyurethane pre-polymer and a curing agent (i.e., polymerization); post curing the polyurethane; optionally grinding the material to generate a post cured polyurethane polymer in granulated form; extruding the post cured and/or optionally granulated polyurethane polymer; and optionally pelletizing the extruded TPU.

In an embodiment, the TPU composition may be generated by a process in which a pre-polymer is mixed with a curing agent at temperatures of from about 50° C. to about 150° C. to form a polymer. The method may then include heating the polymer at temperatures from about 50° C. to about 200° C. for about 1 to about 24 hours to obtain a post-cured polymer. The post-cured polymer may then optionally be ground to generate a granulated polymer. Optionally, the method may further include processing either the post-cured polymer or the granulated polymer in an extruder at temperatures from about 150° C., or higher, to yield a TPU composition. Further operations may optionally include pelletizing the TPU composition, re-melting the pelletized TPU composition, and extruding the melted TPU composition.

Disclosed methods may further include generating TPU compositions containing optional additives. In an embodiment, optional additives may include antioxidants (including phenolics, phosphites, thioesters, and/or amines), antiozonants, thermal stabilizers, inert fillers, lubricants, inhibitors, hydrolysis stabilizers, light stabilizers, hindered amine light stabilizers, UV absorbers (e.g., benzotriazoles), heat stabilizers, stabilizers to prevent discoloration, dyes, pigments, inorganic and organic fillers, organosulfur compounds, thermal stabilizers, reinforcing agents, and combinations thereof.

Disclosed methods include generating TPU compositions containing optional additives in effective amounts customary for each respective additive. In various embodiments, such optional additional additives may be incorporated into the components of, or into the reaction mixture for, the preparation of the TPU composition. In other embodiments, a base TPU composition lacking optional additives may be generated and optionally processed. Optional processing operations may include grinding TPU materials to generate a granulated material, or to form a powdered base TPU composition material to which optional additives may then be mixed prior to further processing.

In other embodiments, powdered mixtures including a base TPU composition and optional additives may be mixed, melted, and extruded to form a composition. In other embodiments, the TPU composition may be prepared through a reactive extrusion process wherein pre-polymer, curing agent, and any optional additives are fed directly into an extruder, and then are mixed, reacted, and extruded at an elevated temperature. Various alternative combinations of these formulation operations may also be employed in various embodiments.

Further embodiments may include many different types of polymer additives. Such additives may include an acid scavenger, an antiblock, an anti-fogging agent, an antioxidant/heat stabilizer, a blowing agent, a compatibilizer/adhesion promotor, a conductivity enhancer, a flame retardant, a fragrance, an impact modifier, a light diffuser, a nucleating/clarifying agent, an optical brightener, a pigment, a slip agent/lubricant/mold release/processing aid, a UV protector/light stabilizer, a filler, reinforcements/coupling agents, etc.

An antioxidant/heat stabilizer, as described above, helps to prevent degradation via oxidation, especially at elevated temps. An antistatic agent helps dissipate static electricity. Such additives may be advantageous for use in oilfield applications. A blowing agent creates a cellular (foamed) structure within the polymer which tends to reduce density, increases thermal and acoustic insulation, and increases stiffness. A compatibilizer/adhesion promotor helps to create more stable phase morphologies between blended polymers. Such a compatibilizer/adhesion promotor may be useful for embodiments in which a TPU is blended with another type of plastic. A slip agent/lubricant/mold release/processing aid, as described above helps the polymer flow into and release from the mold during processing. Such materials may include fluoropolymers which may be used for casting urethanes. A UV protector/light stabilizer, as described above, helps prevent photodegradation from interaction of UV light with TPU materials. Fillers reinforcements/coupling agents, as described above, are used for strengthening, stiffening, and increased processability of the TPU material. Fillers may include glass fibers, aramid fibers, carbon fibers, etc. Use of aramid and carbon fibers may affect the optical properties of the material and, as such, may influence to degree to which a particular material may be used for laser welding.

Articles of Manufacture

Disclosed embodiments include apparatus, articles of manufacture, and products generated using TPU compositions. Non-limiting example embodiments may include coatings or adhesives, and/or articles having a predetermined three-dimensional structure upon curing after being cast or extruded into a mold. Disclosed embodiments provide TPU compositions that may exhibit significantly higher load bearing properties than other materials based on natural and synthetic rubber, for example.

In various embodiments, articles generated from disclosed TPU compositions may be thermostable. In this regard, although thermoplastics may generally be re-melted and reformed, articles produced from disclosed TPU compositions may exhibit resistance to effects resulting from thermal strain at temperatures sufficiently lower than a melting temperature. For example, articles generated from disclosed TPU compositions may retain their shape (i.e., they may exhibit modulus retention) at elevated temperatures corresponding to service conditions, including temperatures in a range from about 170° C. to about 200° C. Disclosed TPU compositions may be used to form articles that may retain their structure, mechanical strength, and overall performance at elevated temperatures.

Disclosed TPU compositions may exhibit thermal stability in a temperature range from about 160° F. to about 210° F. Embodiment TPU compositions may also exhibit thermal stability for temperatures in a range from about 170° F. to about 200° F., while further embodiments may exhibit thermal stability for temperatures in a range from about 175° F. to about 195° F. Disclosed embodiments may also provide a TPU composition that may exhibit thermal stability for temperatures near 180° F. In one embodiment, the polymer compositions have a Vicat softening measured by ISO 306 or ASTM D1525 is above 220° F.

Disclosed embodiments include TPU compositions having favorable mechanical properties, as characterized by cut/tear/abrasion resistance data, relative to known thermoplastic compositions. In certain embodiments, improved properties may include: greater tear strength, better modulus retention at high temperature, low compression set, improved retention of physical properties over time and upon exposure to harmful environments. Certain embodiments provide TPU compositions that may have a combination of improved characteristics such as superior thermal stability, abrasion resistance, and chemical resistance (e.g., to oils and grease). In certain embodiments, articles generated from disclosed TPU compositions may have characteristics that are highly desirable for oil, gas, chemical, mining, automotive, and other industries.

In an exemplary embodiment, an example TPU composition, provided in pellet form, may be loaded into a cylinder of an injection press. Once loaded into the cylinder, the pellet may be heated for a period of time to thereby melt the TPU composition material. The injection press may then extrude the melted exemplary TPU composition material into a mold cavity according to a predetermined injection rate. The injection press may be adapted to include specialized tips and/or nozzles configured to achieve a desired injection output.

Various parameters may be controlled or adjusted to achieve desired results. Such parameters may include, but are not limited to, barrel temperature, nozzle temperature, mold temperature, injection pressure, injection speed, injection time, cooling temperature, and cooling time.

In an embodiment method, barrel temperatures of an injection molding apparatus may be chosen to range from about 148° C. to about 260° C., from about 176° C. to about 233° C., from about 204° C. to about 233° C., from about 210° C. to about 227° C., and from about 215° C. to about 235° C. Nozzle temperatures of an injection molding apparatus may be chosen to range from about 204° C. to about 260° C., from about 218° C. to about 246° C., from about 234° C. to about 238° C., and from about 229° C. to about 235° C.

In an embodiment method, injection pressure of an injection molding apparatus may be chosen to range from about 10,000 psi to about 15,000 psi. In further embodiments, injection pressures may be considerably higher. In still further embodiments the injection pressure is about 30,000 psi. Injection speed of an injection molding apparatus may be chosen to range from about 1.0 cubic inch/second to about 3.0 cubic inch/second, from about 1.5 cubic inch/second to about 2.5 cubic inch/second, from about 1.75 cubic inch/second to about 2.5 cubic inch/second, and from about 2.1 cubic inch/second to about 2.4 cubic inch/second. For fine mesh injection the speed is about 5.0 cubic inch/second to about 7.0 inch/second, from about 5.5 cubic inch/second to about 6.5 cubic inch/second, from about 5.0 cubic inch/second to about 6.0 cubic inch/second.

In an embodiment method, injection time may be chosen to range from about 0.25 seconds to about 3.00 seconds, from about 0.50 second to about 2.50 seconds, from about 0.75 seconds to about 2.00 seconds, and from about 1.00 second to about 1.80 seconds. Moreover, the injection time may be modified to include a “hold” for a certain period of time in which injection is paused. Hold periods may be any particular time. In an exemplary embodiment, the hold time may range from 0.10 seconds to 10.0 minutes. Other hold times may be use in other embodiments.

In an embodiment method, mold temperatures may be chosen to range from about 37° C. to about 94° C., from about 43° C. to about 66° C., and from about 49° C. to about 60° C. Cooling temperatures may be gradually reduced to control curing of a disclosed TPU composition. The temperature may be gradually reduced from that of the mold temperature to ambient temperature over a period of time. The time period for cooling may be chosen to be virtually any time period ranging from second to hours. In an embodiment, the cooling time period may range from about 0.1 to about 10 minutes.

The following method describes an injection molding process that generates screening members based on disclosed TPU compositions. As described above, TPU compositions may be formed as TPU pellets. The TPU composition material may first be injected into a mold that is designed to generate a screening member. The TPU composition may then be heated to a temperature suitable for injection molding to thereby melt the TPU material. The melted TPU material may then be loaded into an injection molding machine. In an embodiment, the mold may be a two-cavity screening member mold. The mold containing the injected melted TPU material may then be allowed to cool. Upon cooling, the TPU material solidifies into a screening member shape defined by the mold. The resulting screening members may then be removed from the mold for further processing.

Embodiments of the present disclosure provide injection molded screen elements that are of a practical size and configuration for manufacture of vibratory screen assemblies and for use in vibratory screening applications. Several important considerations have been taken into account in the configuration of individual screen elements. Screen elements are provided that: are of an optimal size (large enough for efficient assembly of a complete screen assembly structure yet small enough to injection mold (micro-mold in certain embodiments) extremely small structures forming screening openings while avoiding freezing (i.e., material hardening in a mold before completely filling the mold)); have optimal open screening area (the structures forming the openings and supporting the openings are of a minimal size to increase the overall open area used for screening while maintaining, in certain embodiments, very small screening openings necessary to properly separate materials to a specified standard); have durability and strength, can operate in a variety of temperature ranges; are chemically resistant; are structural stable; are highly versatile in screen assembly manufacturing processes; and are configurable in customizable configurations for specific applications.

Embodiments of the present disclosure provide screen elements that are fabricated using extremely precise injection molding. The larger the screen element the easier it is to assemble a complete vibratory screen assembly. Simply put, the fewer pieces there are to put together, the easier the system will be to put together. However, the larger the screen element, the more difficult it is to injection mold extremely small structures, i.e. the structures forming the screening openings. It is important to minimize the size of the structures forming the screening openings so as to maximize the number of screening openings on an individual screen element and thereby optimize the open screening area for the screening element and thus the overall screen assembly. In certain embodiments, screen elements are provided that are large enough (e.g., one inch by one inch, one inch by two inches, two inches by three inches, one inch by six inches etc.) to make it practical to assemble a complete screen assembly screening surface (e.g., two feet by three feet, three feet by four feet, etc.). The relatively “small size” (e.g., one inch by one inch, one inch by two inches, two inches by three inches, etc.) is fairly large when micro-molding extremely small structural members (e.g., opening sizes and structural members as small as 43 microns). The larger the size of the overall screen element and the smaller the size of the individual structural members forming the screening openings, the more prone the injection molding process is to errors such as freezing. Thus, the size of the screen elements must be practical for screen assembly manufacture while at the same time small enough to eliminate problems such as freezing when micro-molding extremely small structures. Sizes of screening elements may vary based on the material being injection molded, the size of the screening openings required and the overall open screening area desired.

In embodiments of the present invention a thermoplastic is used to injection mold screen elements. As opposed to thermoset type polymers, which frequently include liquid materials that chemically react and cure under temperature, use of thermoplastics is often simpler and may be provided, e.g., by melting a homogeneous material (often in the form of solid pellets) and then injection molding the melted material. Not only are the physical properties of thermoplastics optimal for vibratory screening applications but the use of thermoplastic liquids provides for easier manufacturing processes, especially when micro-molding parts as described herein. The use of thermoplastic materials in the present invention provides for excellent flexure and bending fatigue strength and is ideal for parts subjected to intermittent heavy loading or constant heavy loading as is encountered with vibratory screens used on vibratory screening machines. Because vibratory screening machines are subject to motion, the low coefficient of friction of the thermoplastic injection molded materials provides for optimal wear characteristics. Indeed, the wear resistance of certain thermoplastics is superior to many metals. Further, use of thermoplastics as described herein provides an optimal material when making “snap-fits” due to its toughness and elongation characteristics. The use of thermoplastics in embodiments of the present invention also provides for resistance to stress cracking, aging and extreme weathering. The heat deflection temperature of thermoplastics is in the range of 200° F. With the addition of glass fibers, this will increase from approximately 250° F. to approximately 300° F. or greater and increase rigidity, as measured by Flexural Modulus, from approximately 400,000 PSI to over approximately 1,000,000 PSI. All of these properties are ideal for the environment encountered when using vibratory screens on vibratory screening machines under the demanding conditions encounter in the field.

In this way, screen elements are provided that: are of an optimal size (large enough for efficient assembly of a complete screen assembly structure yet small enough to injection mold (micro-mold in certain embodiments) extremely small structures forming screening openings while avoiding freezing (i.e., material hardening in a mold before completely filling the mold)); have optimal open screening area (the structures forming the openings and supporting the openings are of a minimal size to increase the overall open area used for screening while maintaining, in certain embodiments, very small screening openings necessary to properly separate materials to a specified standard); have durability and strength, can operate in a variety of temperature ranges; are chemically resistant; are structurally stable; are highly versatile in screen assembly manufacturing processes; and are configurable in customizable configurations for specific applications.

Further, screening elements, subgrids, and screen assemblies may have different shapes and sizes as long as structural support members of subgrids are provided to support corresponding reinforcement members of screening elements. Screens, subgrids, and screen assemblies are designed to withstand high vibratory forces (e.g., accelerations in a range of 3-9G), abrasive materials (e.g., fluids having several percent to up to 65 percent abrasive solids) and high load demands (e.g., fluids having specific gravity up to 3 pounds per gallon). Screen assemblies are also designed to withstand up to 2000-3000 lb compressive loading of screen assembly edges as described, for example, in U.S. Pat. Nos. 7,578,394 and 9,027,760, the entire disclosure of each of which is hereby incorporated by references. Further, the disclose screening assemblies are designed so that a size of screening openings is maintained under service conditions including the above-mentioned compressive loading, high vibratory forces, and in the presence of heavy fluids

Development of Suitable Compositions

The above-described embodiments provide TPU compositions expressed in ranges of the various components. Improved materials were obtained by varying the composition of TPU materials and percentages of fillers, flow agents, and other additives. Screening members were generated using injection molding processes based on the various compositions. The screening members were attached to subgrid structures and assembled into large-area screening assemblies that were used in field testing applications.

FIG. 4 illustrates an example screening assembly that was generated from screening members and subgrid structures as described above with reference to FIGS. 1 to 3A, according to disclosed embodiments.

FIG. 5 illustrates results of actual field testing of screening assemblies, accord to an embodiment. The data presented in FIG. 5 represents results of testing embodiment screening assemblies for screening materials produced during oil and gas exploration at depths extending to at least about 100,000 feet±5,000 feet. The best performing composition BB had a glass fiber (10 μm diameter) content of about 7%, while the next-best performing composition BA had a glass fiber (10 μm diameter) content of about 5%. Each composition also had flow agent content of about 0.5%, and a heat stabilizer content of about 1.5%. The screen element surface elements 84 (e.g., see FIG. 2) had thickness T about 0.014 inch in all of the tests for which results are presented in FIG. 5.

In additional embodiments, screening members having surface elements 84 having smaller thicknesses including T=0.007 inch, 0.005 inch, and 0.03 inch, where generated. For large bar thickness, for example, 0.014 inch, a larger amount of glass filler can be added whereas for intermediate thicknesses, i.e., 0.005 inch and 0.007 inch a lesser amount of filler is necessary to sufficiently stiffen the structure while still allowing for facile injection molding. For elements having a small bar thickness, for example, 0.003 inch, a small amount of filler is necessary. For these embodiments, it was advantageous to use lower concentrations of filler, flow agent, and thermal stabilizers as shown in Table 1 below.

TABLE 1 T = T = T = T = 0.014 inch 0.007 inch 0.005 inch 0.003 inch filler   7%   5%   3%   2% heat 1.5% 1.5% 1.13% 0.85% stabilizer flow agent 0.5% 0.5% 0.38% 0.28%

As features sizes are reduced, it may be advantageous to include higher filler percentages to allow the material to better fill all spaces in the mold. Tables 2, 3, 4, and 5, show filler percentages that were found to be advantageous for various screen opening widths W, for each of the four values of T shown above in Table 1.

Table 2 shows filler percentages as a function of screen opening width W for screen opening thickness T=0.014 inch.

TABLE 2 W > 0.0046 in 0.0046 in > W > 0.0033 in W < 0.0033 in filler 0.0% 0.0% 0.0%

Thus, for T=0.0014 in, all values of W in the above recited ranges may be manufactured with virgin material (i.e., no filler).

Table 3 shows filler percentages as a function of screen opening width W for screen opening thickness T=0.007 inch.

TABLE 3 W > 0.0046 in 0.0046 in > W > 0.0033 in W < 0.0033 in filler 0.0% 2.5% or greater 5.0% or greater

Table 4 shows filler percentages as a function of screen opening width W for screen opening thickness T=0.005 inch.

TABLE 4 W > 0.0046 in 0.0046 in > W > 0.0033 in W < 0.0033 in filler 0.0% 2.5% or greater 5.0% or greater

Table 5 shows filler percentages as a function of screen opening width W for screen opening thickness T=0.003 inch.

TABLE 5 W > 0.0046 in 0.0046 in > W > 0.0033 in W < 0.0033 in filler 5.0% or greater 5.0% or greater 5.0% or greater

A variety of screen elements having a range of sizes for length L, width W, and thickness T, were generated using the above-described compositions, as shown below in Tables 6 to 9 below.

Table 6 illustrates the percent open area of example embodiments of screen elements with fixed thickness T=0.014 in, fixed length L=0.076 in, and variable width W.

TABLE 6 mesh W (in) T (in) L (in) % open area 80 0.0071 0.014 0.076 23.3 100 0.0059 0.014 0.076 20.3 120 0.0049 0.014 0.076 17.6 140 0.0041 0.014 0.076 13.4 170 0.0035 0.014 0.076 12.2 200 0.0029 0.014 0.076 10.3 230 0.0025 0.014 0.076 9.1 270 0.0021 0.014 0.076 7.9 325 0.0017 0.014 0.076 6.2

Table 7 illustrates the percent open area of example embodiments of screen elements with fixed thickness T=0.007 in, fixed length L=0.046 in, and variable width W.

TABLE 7 mesh W (in) T (in) L (in) % open area 80 0.0071 0.007 0.046 27.3 100 0.0059 0.007 0.046 25.2 120 0.0049 0.007 0.046 23.1 140 0.0041 0.007 0.046 20.5 170 0.0035 0.007 0.046 18.5 200 0.0029 0.007 0.046 16.5 230 0.0025 0.007 0.046 14.9 270 0.0021 0.007 0.046 12.8 325 0.0017 0.007 0.046 10.1

Table 8 illustrates the percent open area of example embodiments of screen elements with fixed thickness T=0.005 in, fixed length L=0.032 in, and variable width W.

TABLE 8 mesh W (in) T (in) L (in) % open area 80 0.0071 0.005 0.032 31.4 100 0.0059 0.005 0.032 29.3 120 0.0049 0.005 0.032 27.0 140 0.0041 0.005 0.032 24.1 170 0.0035 0.005 0.032 22.0 200 0.0029 0.005 0.032 19.7 230 0.0025 0.005 0.032 16.4 270 0.0021 0.005 0.032 14.7 325 0.0017 0.005 0.032 12.1

Table 9 illustrates the percent open area of example embodiments of screen elements with fixed thickness T=0.003 in, fixed length L=0.028 in, and variable width W.

TABLE 9 mesh W (in) T (in) L (in) % open area 80 0.0071 0.003 0.028 32.2 100 0.0059 0.003 0.028 30.1 120 0.0049 0.003 0.028 27.8 140 0.0041 0.003 0.028 25.2 170 0.0035 0.003 0.028 23.1 200 0.0029 0.003 0.028 20.1 230 0.0025 0.003 0.028 17.2 270 0.0021 0.003 0.028 15.3 325 0.0017 0.003 0.028 13.2

The above-described embodiments relate to varying a filler percentage based on screening opening dimensions T, L, and W. In further embodiments, fiber length and diameter may be varied to determine optimal values of length and diameter as a function of T, L, and W.

In some embodiments, a presence of filler material may affect a materials' durability over time. In certain embodiments, a larger percentage of filler may lead to a shorter lifetime of the material. In this way, for a given application, there may be tradeoff in material properties vs. concentration of filler material. For example, increasing a percentage of filler material may strengthen the material, may help to avoid material shrinkage, and may make the material less prone to sticking to the mold. However, the improvement of mechanical properties must be weighed against the potential for the material to have a reduced lifetime due to the larger percentage of filler.

Further, increasing a percentage of filler material may change the materials' optical properties, which may affect the materials' suitability for use with laser welding. In addition to the percentage of filler material, the choice of filler material may also affect the materials' optical properties. For example, use of carbon fibers may lead to greater optical absorption relative to a material in which glass fibers are used. Further, optical absorption is generally frequency/wavelength dependent. In this regard, darker materials (e.g., materials with carbon fibers) may require the use of longer wavelength laser radiation for laser welding in comparison to lighter materials (e.g., materials with glass fibers).

Further compositions may be provided that do not include fillers, additional heat stabilizers, and/or flow agents. Further, hardness and other properties of the resulting composition may be controlled by appropriate mixing of various materials having different hardness values and other properties. For example, a composition may be provided that includes a mixture of a first thermoplastic polyurethane having a first hardness, and a second thermoplastic polyurethane having a second hardness. In an example embodiment, the first and second thermoplastic polyurethanes may each include a modified ester and the first and second thermoplastic polyurethanes may be chosen to have different hardness values. For example, the first thermoplastic polyurethane may have a hardness of approximately 59 Shore D durometer, and the second thermoplastic polyurethane may have a hardness of approximately 95 Shore A durometer. In this way, a composition having a mixture of the first and second thermoplastic polyurethanes may be generated that has a has a hardness in a range from approximately 95 Shore A durometer to 59 Shore D durometer.

Further compositions, for example, may have a hardness in a range from approximately 48 to 53 Shore D durometer or may have a hardness in a range from approximately 54 to 58 Shore D durometer. Further embodiments may have a variety of hardness values depending on the hardness values of the materials in the mixture and the relative proportions of such materials. For example, a composition may be provided having a 50/50 mixture of the first and second polyurethanes or may have any suitable ratio of first and second polyurethanes depending on the desired properties of the resulting material.

Each of the first and second thermoplastic polyurethanes may be obtained by a process in which a urethane prepolymer, having a free polyisocyanate monomer content of less than 1% by weight, is reacted with a curing agent, and then the resulting material is processed by extrusion at temperatures of 150° C. or higher. The resulting composition may be suitable for use in injection molding of articles that have pore sizes in a range from approximately 35 microns to approximately 150 microns. Such articles may include screen elements having an open screening area in a range from approximately 10% to approximately 35%.

The urethane prepolymer, mentioned above, may be prepared from a polyisocyanate monomer and a polyol comprising an alkane diol, polyether polyol, polyester polyol, polycaprolactone polyol and/or polycarbonate polyol, and the curing agent includes a diol, triol, tetrol, alkylene polyol, polyether polyol, polyester polyol, polycaprolactone polyol, polycarbonate polyol, diamine or diamine derivative.

A disclosed method of manufacturing a screen element may include generating a composition having a thermoplastic polyurethane and injection molding the screen element using the generated composition. The screen element may be injection molded to have openings having a size in a range from approximately 35 microns to approximately 150 microns and to have an open screening area of the screen element in a range from approximately 10% to approximately 35%.

In this method, the composition may be generated by reacting a first thermoplastic polyurethane having a first hardness with a second thermoplastic polyurethane having a second hardness at a temperature greater than about 150° C. The first and second polyurethanes may be chosen to each include a modified ester and to have a specific hardness value. For example, the first thermoplastic polyurethane may have a hardness of approximately 59 Shore D durometer, and the second thermoplastic polyurethane may have a hardness of approximately 95 Shore A durometer. In this way, a composition having a mixture of the first and second thermoplastic polyurethanes may be generated that has a has a hardness in a range from approximately 95 Shore A durometer to 59 Shore D durometer.

In various embodiments, the resulting screen element may have openings having a shape that is approximately rectangular, square, circular, or oval shaped. In other embodiments, the screen element may have openings that are elongated slots having a length L, and width W, separated by surface elements having a thickness T, as described above with reference to FIG. 2, and with reference to Tables 6 to 9. The thickness T of the surface elements, for example, may be in a range from approximately 0.003 inch to 0.020 inch, or the thickness T may be approximately 0.014 inch, 0.007 inch, 0.005, inch, 0.003 inch, etc. The width W of the surface elements, for example, may be in a range from approximately 0.0015 inch to approximately 0.0059 inch in some embodiments, and in further embodiments, a length-to-width ratio L/W of the elongated slots may have a value in a range from approximately 1:1 to approximately 30:1. Further geometric parameters of screen elements may be varied, as described below with reference to FIGS. 6A to 8C and Table 10, and corresponding suitable compositions may be developed having properties that are tailored to specific geometries of articles to be injection molded.

FIGS. 6A to 6C illustrate various views of a screen element 600 that includes screening openings having rounded corners, according to an embodiment. FIG. 6A illustrates a top view of screen element 600 and FIG. 6B illustrates a side view 604 of screen element 600 of FIG. 6A, according to an embodiment. A small portion 602 of screen element 600 of FIG. 6A is shown in an exploded view 606 in FIG. 6C, according to an embodiment. As shown in FIG. 6C, each of the screening openings 608 includes rounded corners. The rounded corners of screening openings 608 act to reduce local stress concentrations that typically form near sharp corners, such as corners of screening openings in other embodiments.

For example, in certain other embodiments, sharp corners may create an increased stress concentration factor near intersection points of the screen surface elements and walls of the screen element. These stress concentration factors may cause premature panel failure. A common point of failure may occur when a surface element breaks away from a wall of the screen element. To extend screen life, a fillet has been added to each of the sharp edges in the embodiments of FIGS. 6A to 6C to yield rounded corners, as shown. The presence of this added fillet reduces geometric discontinuities and leads to a decrease in the intensity of the local stress field where the bars connect to the walls. Additional advantages include improved ease of injection molding by allowing a wider path through which material may travel during filling. The reduction in sharp corners also promises to reduce material shear during injection molding, which may otherwise be a cause of premature material degradation. The advantages of embodiments having rounded corners may possibly be offset by disadvantages including slightly reduced open area caused by the fillets. There may also be a potential for increased blinding due to the decreased slot width due to the presence of the fillets.

FIGS. 7A to 7D illustrate embodiments in which screening apertures may have different orientations, according to an embodiment. FIG. 7A illustrates a top view of a screen element 700 that includes transversely aligned screening openings, according to an embodiment. FIG. 7B illustrates an exploded top view of a portion of the screen element 700 of FIG. 7A showing details of transversely aligned screening openings, according to an embodiment. FIG. 7C illustrates a top view of a screen element 702 that includes longitudinally aligned screening openings, and FIG. 7D illustrates an exploded top view of a portion of the screen element 702 of FIG. 7C showing details of longitudinally aligned screening openings, according to an embodiment.

FIGS. 8A to 8C illustrate cross-sectional views of several embodiment surface elements 84 (e.g., see FIG. 2). Each surface element 84 has a top flat surface 802 having a thickness T. While FIG. 2 presents a top view of a screen element having surface elements 84, each of FIGS. 8A to 8C presents an edge cross-section view of a single surface element 84 viewed from a direction looking right-to-left in the plane of FIG. 2. Thus, a bottom-to-up direction in each of FIGS. 8A to 8C corresponds to a direction perpendicular to the screen element surface of FIG. 2. The surface elements in FIGS. 8A to 8C respectively have thicknesses T of 0.007 inch, 0.005 inch, and 0.005 inch. Surface elements 84 may have various geometries extending into the surface (i.e., downwardly in FIGS. 8A to 8C). Surface elements 84 in each of FIGS. 8A to 8A have a tapered shape, although surface elements 84 may have many other shapes in other embodiments.

Surface elements 84 in FIGS. 8A and 8B each have a tapered shape having flat side surfaces 804 that are inclined at an angle relative to a vertical direction (i.e., an up-down direction in FIGS. 8A, 8B, and 8C). In this regard, the surfaces 804 in FIG. 8A subtend an angle 806 of approximately 15 degrees, while surfaces 804 in FIG. 8B subtend an angle 806 of approximately 12 degrees. In the geometry of FIGS. 8A and 8B, the surface thickness T and angle 806 of the surface element 84 side edges 804 determines a depth 808 of the surface elements 84 into the surface. In this example, surface element 84 of FIG. 8A extends to a depth 808 of approximately 0.015 inch, while surface element 84 of FIG. 8B extends to a depth 808 of approximately 0.009 inch. Bottom edges 810 of surface elements 84 in FIGS. 8A and 8B may have various geometries. In this example, surface elements 84 of FIGS. 8A and 8B each have a rounded shape characterized by a radius of curvature. The radius of curvature of surface elements 84 in FIGS. 8A and 8B is approximately 0.0018 inch.

FIG. 8C illustrates a surface element having a different geometry from that of FIGS. 8A and 8B. In this regard, side edges of surface element 84 in FIG. 8C may have a dual-taper design. A first portion 812 of side edges of surface element 84 in FIG. 8C may subtend a first angle 814, while a second portion 816 of side edges of surface element 84 in FIG. 8C may subtend a second angle 818. For example, first portion 812 may subtend an angle 814 of approximately 15 degrees and extend to a depth 820 of approximately 0.004 inch. Similarly, second portion 816 may subtend an angle of approximately 4 degrees and extend to a depth 822 of approximately 0.008 inch. In this example, first 812 and second 816 portions together extend to a depth 824 of approximately 0.012 inch. As with surface elements 84 of FIGS. 8A and 8B, surface element 84 of FIG. 8C may have a rounded bottom edge 810 characterized by a radius of curvature. In this example, bottom edge 810 of surface element 84 of FIG. 8C has a radius of curvature of approximately 0.0018 inch.

A comparison of FIGS. 8B and 8C shows that surface element 84 of FIG. 8C extends to a greater depth (i.e., approximately 0.012 inch) than surface element 84 of FIG. 8B (i.e., extending to approximately 0.008 inch). The greater depth of surface element 84 of FIG. 8C may allow surface element 84 of FIG. 8C to have greater strength than surface element 84 of FIG. 8B. Second portion 816 has a smaller width than the width of first portion 812. As such, adjacent surface elements 84 having the dual-taper shape of FIG. 8C allow greater space between adjacent surface elements 84 relative to surface elements 84 of FIG. 8B. As such, a screen element having surface elements 84 having a configuration as shown in FIG. 8C may be stronger and may be less prone to blinding (i.e., blocking of screen openings 86 of FIG. 2) relative to a screen element having surface elements 84 of FIG. 8B, due to the additional space between adjacent surface elements 84 of FIG. 8C.

In certain screening applications, it may be advantageous to adapt or alter an amount of, and location of, attachment of screen elements to subgrids. As described above with reference to FIGS. 3 and 3A, a screen element 416 may be attached to a subgrid 414. For example, screen element 416 may be attached to subgrid 414 via laser welding. In this regard, fusion bars 476 and 478 may engage with corresponding cavity pockets 472 (e.g., see FIGS. 1B and 1C) of screen element 416. Application of laser radiation may then be used to melt fusion bars 476 to thereby form a bond between screen element 416 and subgrid 414. In some embodiments, it may be advantageous to melt all of the fusion bars 476 to thereby form a tight connection between screen element 416 and subgrid 414. In other embodiments, it may be advantageous to laser weld only a sub-set of fusion bars 476 to thereby form a less-tight connection between screen element 416 and subgrid 414. Points at which fusion bars 476 are not laser welded to subgrid 414 allow motion of screen element 416 relative to subgrid 414, as described in greater detail below.

FIG. 9 illustrates a top view of a screen element and frame assembly 900 with various regions 901 to 920 that may be laser welded to an underlying subgrid, according to an embodiment. As described above, laser welding all of regions 901 to 920 leads to a strong binding between screen element 900 and subgrid. Such a fully-welded configuration allows little relative motion between screen element 900 and the underlying subgrid. In further configurations, some of the potential laser weld locations (i.e., some of regions 901 to 920) may be left un-welded to allow relative motion between screen element 900 and the underlying subgrid.

In a first example application, a screen element fully bonded to a subgrid would be desirable for a situation in which a screening operation is needed to be performed for dewatering of a high-solids slurry. In such an application, it would be desirable to assure that the screen is completely and securely attached to the support subgrid. In this regard, screen element 900 may be laser welded to the underlying subgrid around a perimeter and across the middle of the screen element including laser welding all regions 901 to 920. Such a configuration would allow the assembly (screen and subgrid) to move as a rigid unit in unison with vibrating motion of the vibrating screening machine. This is especially useful when dewatering heavy solids at high flow rates and at high accelerations (i.e., high G forces). Such solids must be moved quickly along a screening surface. This sometimes occurs at high G forces or large amplitudes of motion at the screen surface. In such a situation, any relative movement of the subgrid and screen surface that is not in sync with the vibrating screening machine may cause a reduction in conveyance of solids and, in turn, a reduction in a flow of material through the screen.

In other situations, it may be desirable to have a screen element that is not fully laser-welded to the underlying subgrid. As such, during operation, relative motion (i.e., 2^(nd) order movement) between the screen element and the subgrid may be beneficial. For example, in a dry screening or sifting application (i.e., attrition screening) a 2^(nd) order movement or vibration of the screen element or surface relative to the subgrid may aid in de-blinding of the screen (i.e., removing particles that may in certain situations become stuck in screen openings). A slight vertical impact or force could be applied in order to dislodge particles that are transitionally retained in the tapered screen openings. Such a situation may occur, for example, in square or slotted screen openings.

For this type of application, it may be beneficial to generate a partially bonded screen element in screen element and frame assembly 900 (e.g., see FIG. 9) by bonding (e.g., via laser welding) regions 905, 906, 907, 901, 909, 910, 912, 913, 915, 916, 917, and 920, while leaving regions 902, 903, 904, 908, 911, 914, 918, and 919 un-bonded. Such a configuration would allow vertical movement of the screen element surface and would aid in dislodging transitionally retained particles form screen element openings due to impacts between screen element 900 and a surface of the subgrid.

FIG. 10 illustrates a vibrational amplitude profile of a screen element 900 that is partially bonded to a subgrid 1000, according to an embodiment. In this example, screen element 900 is bonded to subgrid 1000 to allow movement in only one direction perpendicular to a surface of subgrid 1000. In this configuration, vibrational motion of screen element 900 relative to subgrid 1000 occurs in a direction perpendicular to the surface of subgrid 1000 such that the amplitude has maxima at first 1002 a and second locations 1002 b, as shown in FIG. 10. Further, screen element 900 is bonded to have zero amplitude of relative motion at first 1004 a, second 1004 b, and third 1004 c locations such that screen element 900 moves rigidly with subgrid 1000 at these locations. In this example, vertical motion causes screen element 900 to pull away from subgrid 1000 on an up stoke and to impact subgrid 1000 on a down stroke. As described above, such motion may be useful in dry screening application to aid in de-blinding.

In addition to a bonding configuration of screen element 900 to subgrid 1000 (e.g., see FIGS. 9 and 10), material properties of subgrid 1000 may influence relative motion of screen 900 and subgrid. For example, subgrids 1000 may be configured to be more or less rigid based on thickness and the types of materials used to construct subgrid 1000. As such, it may be desirable to have a subgrid 1000 that is more rigid for applications in which screen element 900 is tightly bonded to subgrid 1000. Alternatively, in other applications, it may be advantageous to have subgrids 1000 that are less rigid to allow more relative motion between subgrid 1000 and partially bonded screen element 900. Further, toughness of subgrid materials may influence relative motion of screen element 900 and subgrid 1000 due to the relative tendency of subgrid materials to absorb more/less vibrational energy for materials having greater/lesser toughness.

In addition to the mechanical properties of the subgrid, the mechanical properties of screen elements may be varied as needed for a given embodiment. For example, as described above, the hardness of the material used to generate screen elements may be chosen based on the composition. A harder material may be desirable for applications requiring the screen element to be tightly secured to the subgrid to prevent relative motion of the screen element. In contrast, a softer material may be more suitable for applications in which the screen element is partially secured to the subgrid, thereby allowing relative motion between the screen element and the subgrid (e.g., see FIG. 10). A such, a softer material may allow increased relative vibrational motion between the screen element and the subgrid relative to a harder material.

As described above, hardness and other properties of the resulting composition may be controlled by appropriate mixing of various materials having different hardness values and other properties. For example, a composition may be provided that includes a mixture of a first thermoplastic polyurethane having a first hardness, and a second thermoplastic polyurethane having a second hardness. For example, the first thermoplastic polyurethane may have a hardness of approximately 59 Shore D durometer, and the second thermoplastic polyurethane may have a hardness of approximately 95 Shore A durometer. In this way, a composition having a mixture of the first and second thermoplastic polyurethanes may be generated that has a has a hardness in a range from approximately 95 Shore A durometer to 59 Shore D durometer. Further embodiments may have a variety of hardness values depending on the hardness values of the materials in the mixture and the relative proportions of such materials. For example, other compositions may have hardness in a range from approximately 48 to 53 Shore D durometer or may have a hardness in a range from approximately 54 to 58 Shore D durometer, as described above.

Example embodiments are described in the foregoing. Such example embodiments, however, should not be interpreted as limiting. In this regard, various modifications and changes may be made thereunto without departing from the broader spirit and scope hereof. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense. The breadth and scope of embodiments of the disclosure should not be limited by any of the above-described example embodiments, but should be defined only in accordance with the following claims and their equivalents.

Conditional language, such as, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain implementations could include, while other implementations do not include, certain features, elements, and/or operations. Thus, such conditional language generally is not intended to imply that features, elements, and/or operations are in any way required for one or more implementations or that one or more implementations necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and/or operations are included or are to be performed in any particular implementation. 

What is claimed is:
 1. A screen element, comprising: i) a first thermoplastic polyurethane having a first hardness; and ii) a second thermoplastic polyurethane having a second hardness; wherein the first and second polyurethanes are combined to form a final thermoplastic polyurethane having a hardness of from approximately 85 Shore A to 59 Shore D; wherein the screen element is a single injection molded piece having a plurality of openings from 38 μm to 150 μm.
 2. The screen element according to claim 1, wherein the first polyurethane and the second polyurethane are formed by: reacting a prepolymer having the formula chosen from:

wherein the index x is from 2 to about 6, the index y is from about 4 to about 25, index z is from about 4 to about 25, and the index n is from 2 to about 8; and wherein further the prepolymer contains less than 0.1% by weight of excess isocyanate moieties; with a curing agent, wherein the curing agent is chosen from polycaprolactone diols, polyglycidyl diols, polylactide diols, polycarabonate diols, polyethylene glycols, polypropylene glycols, or polyalkylene diols.
 3. The screen element according to claim 1, wherein the first thermoplastic polyurethane has a hardness of approximately 59 Shore D durometer, and the second thermoplastic polyurethane has a hardness of approximately 95 Shore A durometer.
 4. The screen element according to claim 1, wherein the hardness of the composition is in a range from approximately 48 to 53 Shore D durometer.
 5. The screen element according to claim 1, wherein the hardness of the composition is in a range from approximately 54 to 58 Shore D durometer.
 6. The screen element according to claim 1, wherein the hardness of the composition is determined by relative proportions of the first and second polyurethanes.
 7. The screen element according to claim 6, wherein the composition is a 50/50 mixture of the first and second polyurethanes.
 8. The screen element according to claim 40, wherein the openings have a shape that is approximately rectangular, square, circular, or oval.
 9. The screen element according to claim 1, wherein the openings are elongated slots having a length L, and width W, separated by surface elements having a thickness T.
 10. The screen element according to claim 9, wherein the thickness T of the surface elements is from approximately 0.003 inch to 0.020 inch.
 11. The screen element according to claim 9, wherein the thickness W of the surface elements is from approximately 0.0015 inch to approximately 0.0059 inch.
 12. The screen element according to claim 9, wherein a length-to-width ratio L/W of the elongated slots is from approximately 1:1 to approximately 30:1.
 13. The screen element according to claim 9, wherein the surface elements have a thickness T that is approximately 0.014 inch.
 14. The screen element according to claim 1, wherein the screen element has an open surface area of from approximately 10% to approximately 35%.
 15. The screen element according to claim 1, wherein the screen element has an open surface area of from approximately 10% to approximately 15%.
 16. The screen element according to claim 9, wherein the surface elements have a thickness T that is approximately 0.007 inch.
 17. The screen element according to claim 9, wherein the surface elements have a thickness T that is approximately 0.005 inch.
 18. The screen element according to claim 9, wherein the surface elements have a thickness T that is approximately 0.003 inch.
 19. The screen element according to claim 18, wherein the screen element has an open surface area of from approximately 30% to approximately 35%.
 20. A screen element, comprising: a thermoplastic polyurethane, the polyurethane formed by reacting a prepolymer with a curing agent.
 21. The screen element according to claim 20, wherein the prepolymer has the formula:

wherein R is a carbon skeleton of 2 to 15 carbon atoms, or a bivalent aromatic radical of 6 to 18 carbon atoms, and R¹ is chosen from:

wherein the index x is from 2 to about 6, the index y is from about 4 to about 25, the index n is from 2 to about
 8. 22. The screen element according to claim 21, wherein the prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about
 8. 23. The screen element according to claim 21, wherein the prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about
 8. 24. The screen element according to claim 21, wherein the prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about
 8. 25. The screen element according to claim 21, wherein the prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about
 8. 26. The screen element according to claim 21, wherein the prepolymer has the formula:

wherein the index x is from 2 to about 6, the index n is from 2 to about
 8. 27. The screen element according to claim 21, wherein the prepolymer has the formula:

wherein the index z is from about 4 to about
 25. 28. The screen element according to claim 21, wherein the prepolymer has the formula:

wherein the index y is from about 4 to about
 25. 29. The screen element according to claim 20, wherein the curing agent is chosen from polycaprolactone diols, polyglycidyl diols, polylactide diols, polycarabonate diols, polyethylene glycols, polypropylene glycols, or polyalkylene diols.
 30. The screen element according to claim 20, wherein the thermoplastic polyurethane has a hardness of from a 85 Shore A durometer value to about a 59 Shore D durometer value.
 31. The screen element according to claim 20, wherein the thermoplastic polyurethane further comprises glass fibers.
 32. The screen element according to claim 31, wherein the amount of glass fibers present is less than about 10% by weight of the thermoplastic polyurethane.
 33. The screen element according to claim 20, wherein the prepolymer contains less than 0.5% by weight of excess isocyanate groups.
 34. The screen element according to claim 33, wherein the prepolymer contains less than 0.1% by weight of excess isocyanate groups.
 35. The screen element according to claim 20, wherein the thermoplastic polyurethane further comprises a heat stabilizer.
 36. The screen element according to claim 35, wherein the heat stabilizer is about 0.1 percent to about 5 percent by weight of the thermoplastic polyurethane.
 37. The screen element according to claim 20, wherein the flow agent is about 0.1 percent to about 5 percent by weight of the thermoplastic polyurethane.
 38. The screen element according to claim 31, wherein the glass fibers have a diameter or width of less than about 20 μm.
 39. The screen element according to claim 20, wherein the screen element is a single injection molded piece including a plurality of openings having a size from approximately 38 μm to approximately 150 μm
 40. The screen element according to claim 39, wherein the openings have a shape that is rectangular, square, circular, or oval.
 41. The screen element according to claim 40, wherein the openings are elongated slots having a length L, and width W, separated by surface elements having a thickness T.
 42. The screen element according to claim 41, wherein the thickness T of the surface elements is from approximately 0.003 inch to 0.020 inch.
 43. The screen element according to claim 41, wherein the thickness W of the surface elements is from approximately 0.0015 inch to approximately 0.0075 inch.
 44. The screen element according to claim 41, wherein a length-to-width ratio L/W of the elongated slots is from approximately 1:1 to approximately 30:1.
 45. The screen element according to claim 41, wherein: the surface elements have a thickness T that is approximately 0.014 inch, and the filler has a concentration of approximately 10% by weight of the thermoplastic polyurethane.
 46. The screen element according to claim 45, wherein the screen element has an open surface area from approximately 10% to approximately 15% of the screen element.
 47. The screen element of claim 41, wherein: the surface elements have a thickness T that is approximately 0.007 inch, and the filler has a concentration of approximately 7% by weight of the thermoplastic polyurethane.
 48. The screen element according to claim 41, wherein: the surface elements have a thickness T that is approximately 0.005 inch, and the filler has a concentration of approximately 5% by weight of the thermoplastic polyurethane.
 49. The screen element of claim 48, wherein the thermoplastic polyurethane further comprises: a heat stabilizer having a concentration of approximately 1.13% by weight of the thermoplastic polyurethane; and a flow agent having a concentration of approximately 0.38% by weight of the thermoplastic polyurethane.
 50. The screen element according to claim 41, wherein: the surface elements have a thickness T that is approximately 0.003 inch, and the filler has a concentration of approximately 3% by weight of the thermoplastic polyurethane.
 51. The screen element according to claim 50, wherein the thermoplastic polyurethane further comprises: a heat stabilizer having a concentration of approximately 0.85% by weight of the thermoplastic polyurethane; and a flow agent having a concentration of approximately 0.28% by weight of the thermoplastic polyurethane.
 52. The screen element according to claim 51, wherein the screen element has an open surface area from approximately 30% to approximately 35%.
 53. A micro-molded screen element, comprising: i) a first thermoplastic polyurethane having a first hardness; and ii) a second thermoplastic polyurethane having a second hardness; wherein the first and second polyurethanes are combined to form a final thermoplastic polyurethane having a hardness of from approximately 85 Shore A to 59 Shore D; wherein the micro-molded screen element is a single injection molded piece having a plurality of openings from 43 μm to 150 μm.
 54. The micro-molded screen element according to claim 53, wherein the screen element is from 1 square inch to about 5 square inches.
 55. The micro-molded screen element according to claim 53, wherein the screen element is from 1 square foot to about 4 square feet.
 56. The micro-molded screen element according to claim 54, wherein a plurality of micro-molded screen elements are fitted together to form a screen assembly. 